1. Field of the Invention
The present invention relates to an image taking apparatus employing a solid-state image-sensing device, and more particularly to a slim image taking apparatus, such as a digital still camera or digital video camera, provided with a zoom tens system.
2. Description of the Prior Art
In recent years, as personal computers and the like become wide-spread, digital still cameras and digital video cameras (hereinafter collectively referred to as digital cameras), which permit easy capturing of image data into digital equipment, have been becoming increasingly popular among individual users. Such digital cameras are expected to continue to become more and more popular into the future as an image data input device.
In general, the im age quality of a digital camera depends on the number of pixels provided in a solid-state image-sensing device, such as CCD (charge-coupled device). Nowadays, digital cameras for general consumers boast of high resolution over one mega pixels, and are closing in on cameras using silver-halide film in image quality. Moreover, even in digital cameras for general consumers, the capability of varying the magnification with which images are taken (i.e., zooming capability) is desired; in particular, optical zooming is desired because it causes minimum image degradation. Furthermore, lately, digital cameras are required not only to offer high image quality but also to be compact, in particular slim so as to be easily portable.
In conventionally proposed zoom lens systems for digital cameras, the most common way to make a digital camera slim is to adopt a so-called collapsible lens barrel. Specifically, when the camera is not used, the lens barrel collapses so as to hold the lenses with minimum distances between them, and, when the camera is used, the lenses move out so as to make the camera ready to photograph. With this construction, it is possible, while maintaining satisfactory optical performance, to reduce the number of constituent lenses and thereby reduce the thickness of the lens barrel in its collapsed state (as exemplified by U.S. Pat. No. 6,498,647).
Another way to make a digital camera slim, i.e., other than by using a collapsible lens barrel, is to arrange a zoom lens system with its lens optical axis parallel to, of all the external faces of the camera body that is, for example, substantially box-shaped, that which has the greatest area. Moreover, as a zoom lens system that offers a large angle of view at the wide-angle end but that nevertheless is compact, there is conventionally known a zoom lens system composed of, from the object side, a first lens unit having a negative optical power, a second lens unit having a positive optical power, and a third lens unit having a positive optical power wherein the first lens unit is kept stationary during zooming (as exemplified by Japanese Patent Application Laid-Open No. 2000-137164). By arranging a zoom lens system like this with its lens optical axis parallel to, of all the external faces of the substantially box-shaped camera body, that which has the greatest area, it is possible to realize a slim digital camera.
For a slim digital camera to be usable, it is required to be slim but nevertheless have its most object-side lens arranged with its optical axis perpendicular to, of all the external faces of the substantially box-shaped camera body, that which has the greatest area. One way to realize this is to bend the optical axis by using a prism in the first lens unit (as exemplified by Japanese Patent Application Laid-Open No. H8-248318).
However, with a construction adopting a collapsible lens barrel, like the one disclosed in U.S. Pat. No. 6,498,687 mentioned above, even though it is possible to achieve slimming-down to a certain degree, there is a limit to reducing the thickness of the lens barrel in its collapsed state. Specifically, the thickness of the lens barrel cannot be reduced to less than the total of the thickness of the lenses themselves, that of the image-sensing device, and that of the optical filter and other components required by the image-sensing device. This makes it impossible to achieve satisfactory slimming-down.
Arranging a zoom lens system, like the one disclosed by Japanese Patent Application Laid-Open No. 2000-137164 mentioned above, with its lens optical axis parallel to, of all the external faces of the substantially box-shaped camera body, that which has the greatest area makes the external shape of the camera elongate, and thus makes the camera extremely difficult to use. Usability may be improved by rotatably fitting the lens barrel so that, when the camera is used, the lens barrel is rotated so as to make the lens optical axis perpendicular to, of all the external faces of the substantially box-shaped camera body, that which has the greatest area. This, however, additionally requires a mechanism for rotating the lens barrel, and thus eventually increases the thickness of the camera. Moreover, extra operations are required to rotate the lens barrel when at the start and end of photographing.
With a so-called positive-led zoom construction, like the one disclosed in Japanese Patent Application Laid-Open No. H8-248318, in which the first lens unit has a positive optical power, it is difficult to achieve zooming with a small number of zooming components, and in fact there are provided as many as four zooming components. This makes the structure of the lens barrel complicated, and thus makes the lens barrel large as a whole including its drive components. This makes the camera as a whole wide, and makes satisfactory slimming-down impossible.